A micro-grid is a localized grouping of power generation, storage, and loads that can be connected to the power distribution system (PDS) to provide an additional control layer integrating intermittent renewable energy resources to the power distribution system. From the point of view of a PDS, a connected micro-grid can be controlled as if it is one entity.
A PDS usually treats the micro-grid as a positive or negative load due to unstable voltage on the micro-grid caused by load or generation variations. Such instability reduces the quality of power supply to the PDS, and requires the PDS to control the variations of the voltage supplied by the micro-grid. However, maintaining the stable voltage supply to the PDS requires sophisticated measurements of the power flow on the entire PDS and the micro-grid, which complicates plugin capability of the micro-grid into the PDS.
For example, some PDSs control the micro-grids by adding compensation signal to voltage regulator and/or emulating a voltage source that requires complex power flow computations. For example, voltage regulation methods described in U.S. Pat. No. 8,710,815 and US 20110316518 regulate output voltage dynamic response by adding compensation to a fast inverter's feedback signal. Controlling the micro-grid with the feedback signal determined by PDS provides an extra burden for the PDS and reduces plug-and-play capabilities of the micro-grids.
In addition, providing voltage-control ancillary service by maintaining power quality is a challenging task for micro-grids, because these small-scale power systems are typically managed by droop controllers. Droop controllers help a micro-grid to maintain power sharing when system states deviate from their nominal values. System state changes make PDS operators unable to predict power quality in a power distribution network with micro-grids.
Accordingly, there is a need for a system and a method for local control of the voltage by the micro-grid resulting in substantially constant voltage supply to the PDS to enable plug and play capability of the micro-grids.